1. Technical Field
The present invention relates to wireless communication, and more particularly, to a method of reporting channel quality, which can reduce error caused by wireless channel environment.
2. Related Art
The GSM (Global System for Mobile communication) is a radio technology which has been developed as a system for standardizing radio communication systems in Europe and which has widely been deployed all over the world. The GPRS (General Packet Radio Service) is introduced to provide a packet switched data service in a circuit switched data service provided from the GSM. The EDGE (Enhanced Data Rate for GSM Evolution) employs the 8-PSK (Phase Shift Keying) instead of the GMSK (Gaussian Minimum Shift Keying) employed in the GSM. The EGPRS (Enhanced General Packet Radio Service) represents the GPRS using the EDGE.
The physical channel dedicated to GPRS/EGPRS traffic is called Packet Data Channel (PDCH). Logical channels such as Packet Common Control Channel (PCCCH), Packet Data Traffic Channel (PDTCH) and Packet Associated Control Channel (PACCH) are mapped to the PDCH. The PCCCH is used for control signaling necessary for initiating packet transfer. The PDTCH is used to transmit user data. The PACCH is used for dedicated signaling.
Unlike a GSM system, an EGPRS system provides multiple data rates. For example, data is transmitted at nine different data rates over the PDTCH. In a process called ‘link adaptation’ , the data rate is adjusted based on channel condition. When the channel condition is good, data can be transmitted at higher data rates. Conversely, when the channel condition is poor, data is transmitted at slower data rates. Transmitting data using a particular modulation and coding scheme (MCS) at a data rate that is too high for the channel condition may result in a loss of data. Link adaptation increases overall data throughput by using highest data rate that can dependably be supported using a particular MCS at given channel condition.
In the EGPRS system, a mobile station needs to report channel quality to a base station. The channel quality between the base station and the mobile station is expressed in terms of a bit error probability (BEP). The BEP is the expected value of the actual Bit Error Rate (BER) of a signal received by the mobile station over the wireless channel. The base station selects appropriate MCS depending on the reported channel quality. Link adaptation can most effectively be performed when the channel quality is reported a BEP that most accurately estimates the actual BER. The BEP is measured by burst-by-burst.
In the EGPRS system, user data and control message may use different modulation scheme. For example, a PDTCH for the user data is modulated with Gaussian Minimum Shift Keying (GMSK) or octal-Phase Shift Keying (8-PSK). A PACCH for the control message is only modulated with GMSK. When the PDTCH is continuously modulated with 8-PSK and a mobile station measures a BEP for the PDTCH, the base station may select inappropriate MCS because the mobile station only reports the BEP based on 8-PSK.
A method is sought for determining a BEP that can represent various channel condition. Moreover, a method is sought for improving efficiency of link adaptation by reporting a BEP that can represent various channel condition.